1. Technical Field
The present invention relates to a wireless communication apparatus and subcarrier allocation method. More particularly, the present invention relates to a wireless communication method and subcarrier allocation method combining adaptive modulation and frequency scheduling.
2. Description of the Related Art
A multi-user adaptive modulation OFDM system is a system for carrying out effective scheduling for an entire system according to a propagation path of each mobile station. Specifically, a base station apparatus is constituted by a system for allocating a plurality of subcarriers appropriate for each user based on channel quality (frequency division user multiplexing), and selecting appropriate modulation coding schemes (hereinafter referred to as “MCS”) for each subcarrier. Namely, a base station apparatus is capable of carrying out multi-user high-speed data communication by allocating subcarriers in a manner that is the most effective utilization of frequency capable of satisfying the communication quality (for example, minimum transmission rate, error rate) desired by each user based on channel quality, selecting MCS to ensure maximum throughput for each subcarrier, and carrying out data transmission. In this way, in a multi-user adaptive modulation OFDM system such as, for example, “MC-CDM Method Using Frequency Scheduling,” Technical Report of the Institute of Electronics Information and Communication Engineers of Japan, RCS2002-129, July 2002, pp. 61-pp. 66), a reporting method for reporting channel quality information from each mobile station to a base station apparatus is proposed.
An MCS selection table decided in advance is used in the selection of MCS. An MCS selection table shows correspondence between reception quality such as CIR (Carrier to Interference Ratio) etc. and error rates such as packet error rate (hereinafter referred to as “PER”) or bit error rate (hereinafter referred to as “BER”) etc. for each MCS modulation scheme and error encoding scheme. An MCS of a maximum speed capable of satisfying the desired error rate is then selected based on measured reception quality in MCS selection.
However, in the related art, in frequency division user multiplexing, each mobile station reports channel quality information for all subcarriers to a base station apparatus. FIG. 1 shows a reporting format of signal to noise ratio (hereinafter referred to as “SNR”) of channel quality information reported from a mobile station to a base station apparatus of the related art, and FIG. 2 is a view showing a relationship between SNR report bits and modulation scheme. As shown in FIG. 1, the base station apparatus allocates subcarriers and performs adaptive modulation by receiving notification of SNR report bits for every subcarrier in subcarrier order from each communication terminal apparatus for all subcarriers in the communication band. In this event, in the case that transmission by 64QAM adopted as a modulation scheme satisfying the desired transmission rate and PER is required, the base station apparatus selects the first or fifth subcarrier for which an SNR report bit is 3, and allocates packet data employing 64QAM to the first or fifth subcarrier.
However, with the base station apparatus and subcarrier allocation method of the related art, each mobile station reports channel quality information for all subcarriers to the base station apparatus, regardless of whether only some of the subcarriers of all of the subcarriers within the communication band are used. The amount of channel quality control information therefore becomes extremely large in accompaniment with increase in the number of mobile stations and number of subcarriers, and communication efficiency therefore falls.